Probing a pseudoscalar at the LHC in light of $R(D^{(\ast )})$ and muon g-2 excesses

Abstract

We study the excesses of $R(D^{(\ast )})$ and muon $g-2$ in the framework of a two-Higgs-doublet model with top quark flavor-changing neutral-current (FCNC) couplings. Considering the relevant theoretical and experimental constraints, we find that the $R(D^{(\ast )})$ and muon $g-2$ excesses can be simultaneously explained in a parameter space allowed by the constraints. In such a parameter space the pseudoscalar ($A$) has a mass between 20 GeV and 150 GeV so that it can be produced from the top quark FCNC decay $t\to Ac$. Focusing on its dominant decay $A\to \tau \bar{\tau }$, we perform a detailed simulation on $pp\to t\bar{t}\to WbAc\to jjbc\tau \bar{\tau }$ and find that the $2\sigma$ upper limits from a data set of 30 (100) fb${}^{-1}$ at the 13 TeV LHC can mostly (entirely) exclude such a parameter space.

Comments: 20 pages, 4 figures; added references